by Keith Tilley and David Kennedy, P.L.(Eng.), LEED AP
Offsite construction is becoming more prevalent in Canada due to its increased efficiency on jobsites, labour shortage, and tight project timelines. The market for prefabrication modular building systems is expected to rise as more sustainable building standards are implemented because offsite applications create less waste and use less energy. Further, the shift toward factory-based building construction techniques is increasing demand for panelized or volumetric systems due to inherent cost savings.
Collaboration with designers and contractors to facilitate procurement and integration of modular systems is important to offsite construction projects. Price normalization and stakeholder integration is also essential to understanding the full benefits of offsite construction during the estimating and design phases of a project.
Prefabrication in its simplest form is assembling components offsite in a controlled environment, prior to installing onsite. On some level, it can apply to almost all types of buildings, whether it is mechanical systems, panelized walls, bathrooms, or fully finished volumetric boxes. Due to the more frequent use of prefabricated components, new technology and ideas have made offsite manufacturing easier to implement onsite.
The stages at which prefabrication systems are considered in a project determine how much of a building can be efficiently produced offsite. The flexibility of premanufactured solutions is a strong driver for designers, as it does not have to be an all or nothing approach. Many firms are dipping a toe into new building methods by implementing some portion or facet of premanufactured solutions to their building designs. Critical path items, such as building envelope and roofing systems, are commonly selected for offsite construction. It is the creativity of the offsite solutions provider to design a system that does not alter the original design of a building with traditional methods in mind. An example of this hybrid approach is the exterior envelope. In this case, the building structure, design, and esthetic can be achieved as designed, while reducing the timeline, waste, congestion, and risk of a project.
Prefabrication is not a one-size fits all solution. It tends to work best on projects with the scale to take advantage of mass production and repeatability. This does not mean the building has to be boxy or boring. However, if there is a repeatable pattern, factory-built solutions become much more efficient and thereby reduce costs.
The cost of prefabrication
Most stakeholders can grasp and accept the idea of prefabrication. After all, cars and most of the goods used daily are built in a factory. Why then, does it not make financial sense to engage modular construction techniques? A few factors in the construction market contribute to the cost of prefabricated solutions being equal to, or sometimes, slightly higher than in-situ building methods.
Prefabrication requires a large factory to build and store the products. This space is typically a leased or owned space adding overheads to the manufacturer that is included in the product cost. This is in contrast to sub-trades who may have little or no overheads. As prefabrication becomes mainstream, this overhead burden will decrease.
Anything fabricated in a factory must eventually get installed onsite. This requires large transport trucks and trailers. Transportation is expensive, a cost traditional construction methods do not have to include in their price, as suppliers will often ship directly to site or raw materials can be delivered by contractors using pickup trucks or cargo vans depending on the size of the project.
Creating an accurate budget when comparing traditional construction methods to prefabrication is difficult. Getting a true apple-to-apple comparison requires a deep understanding of what is included and excluded when procuring offsite solutions. In most cases, sub-trades will provide an approximate estimate for the entire scope. This estimate will have to be broken down into individual scopes to evaluate the prefabrication option. This technique works in theory, however not engaging all parties to collaborate and provide clarity of precisely what is included in their scope of work, generally leads to skewed numbers. During the estimating and procurement process, documents must be clear and concise to facilitate a true comparison of offsite versus onsite work.
Prefabricated building systems must be designed to a higher standard because there is less ability to adjust onsite and is often inspected more than once during the cycle. This results in a slight increase in cost due to extra strapping or a more rigid frame to undergo dynamic loads during transportation to and from the manufacturing site. In the case of modular bathroom systems, the unit will undergo quality assurance/control (QA/C) testing in the factory and again onsite when the product is connected to the overall building systems. In-situ built bathroom systems usually require an inspection only during rough-in and as the final fixture installation stage.
The implementation of prefabrication for a project requires higher level of understanding from all stakeholders. From the owner’s vision to the building site team, the process and factors that must be considered are new and require looking at a project through a different set of lenses. Prefabrication transforms a construction site from a place where structures are built to one where large pieces or components are erected. There is a fundamental difference in those activities. Taking the building process offsite and simply placing the finished product on a site has many positive advantages to the net cost of a project that are less obvious to calculate when filling out an estimate or pro-forma.
By using prefabrication methods, the overall cost of risk for a project is minimized due to the drastic reduction of exposure. Conventionally, a project’s biggest risk is safety. In certain conditions, traditional construction methods are inherently dangerous, and despite great strides made in the past few decades, injury, lost-time accidents, and death are still prevalent in construction. According to the 2018 Report on Work Fatality and Injury Rates, there were 204,682 loss-time injuries in Canada in 2016. Prefabrication takes many of the higher risk trades, such as drywall and cladding installation, away from the active site and places them in a factory environment where the conditions and risks are more predictable and easier to monitor. This reduction in risk is a long-term benefit for all stakeholders. However, it is hard to quantify the cost of this risk when evaluating the procurement of prefabricated products.